Our investigations have demonstrated that the basic oligopeptide antibiotic edeine, produced by Bacillus brevis Vm4, inhibits replicative bacterial DNA synthesis in vivo and in vitro. It does not inhibit DNA polymerases I and III from E. coli. At bacteriostatic concentrations, edeine does not inhibit the growth of some DNA-containing coliphages. Initiation of protein synthesis is another independent target of edeine. Edeine binds to the 30S ribosomal subunit and prevents the formation of the 30S initiation complex. Edeine has no effect on the synthesis of RNA. The effect of edeine is specific, i.e., it is readily distinguishable from polycationic effects related to the chemical nature of the antibiotic. Our research is aimed at determining the step(s) at which edeine inhibits bacterial DNA synthesis. Cells of the producing strain are impermeable to edeine; in in vitro systems derived from the producing cells, edeine inhibits replicative DNA synthesis and initiation of protein synthesis. Edeine exists in the producing cell in the form of a biologically-inactive complex with membrane components. Treatment of the complex with alkai releases the active antibiotic. Edeine is apparently released into the medium from this complex and this is why intracellular concentration of the active antibiotic is negligible. We are examining the nature of the complex and the kind of bond it forms with edeine.